When behavior thought to be characteristic of humans alone, is found in other animals using carefully controlled experiments, it may not be necessary to posit complex theories that are difficult to test. In the present proposal we will investigate in pigeons a phenomenon that when studied by social psychologists has been attributed to a form of cognitive dissonance called the justification of effort. Specifically, social psychologists have found that greater value is attributed to rewards that have required greater effort to obtain (Aronson &Mills, 1959). This effect has been thought to depend on the human need to resolve the presumed dissonance engendered by the exertion greater effort to obtain comparable rewards. However, we have found that animals (pigeons) will demonstrate a similar effect. They reliably prefer stimuli associated with food if those stimuli are preceded by a high effort response over those preceded by a low effort response. We have interpreted the effect as a form of contrast in which the larger change in value that follows greater effort is preferred over the smaller change in value that follows less effort. We propose: (1) to test this theory against an alternative hypothesis, delay reduction, which proposes that the stimulus preference results from the relative reduction in delay to reinforcement signaled by the stimulus that follows high effort (because it requires a longer time to produce), (2) to obtain a quantitative measure of the trade-off between a smaller amount of food and the preference that comes from greater effort (these experiments will allow us to specify parameters of the model more precisely), (3) to explore the possible adaptive value of this phenomenon by determining whether this form of contrast can actually increase the preference for a less preferred food, (4) to examine the mechanism by which this phenomenon may be adaptive in nature (does food eaten when more hungry become inherently more rewarding, in other contexts, than food eaten when less hungry), (5) to determine if prior experience with less effort in obtaining food will magnify the contrast effect (i.e., examine the role of learning in this contrast effect), (6) to track the development of the contrast effect to determine the optimal amount of training needed to observe its effect and determine if that training can be accelerated. This research has important applied implications. In institutional and educational settings it is important to have sustained, effective reinforcers. Thus, the value of reinforcers may be enhanced by increasing the effort required to obtain them. PUBLIC HEALTH RELEVANCE: The proposed research will investigate the effect of prior events such as effort on the value of reinforcers that follow. To produce healthy behavior, particularly in institutional and educational settings, it is important to have sustained, effective reinforcers. If prior effort or other prior less preferred events affect the value of the reinforcer that follows, it suggests that the value of reinforcers may be enhanced by increasing the effort required to obtain them.